1. Field of the Invention
The application relates to a method utilized in a wireless communication and a communication device thereof, and more particularly, to a method of handling system information reception in a wireless communication system and a related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
In the LTE system, a UE applies system information acquisition procedure to acquire system information broadcasted by the E-UTRAN upon selecting (e.g. upon power on) and upon re-selecting a cell, after handover completion, after entering E-UTRA from another RAT, upon return from out of coverage, upon receiving a notification that the system information has changed, upon receiving an indication about the presence of an Earthquake and Tsunami Warning System (ETWS) notification, upon receiving an indication about the presence of a Commercial Mobile Alert System (CMAS) notification, etc. Note that, unless explicitly stated otherwise the system information acquisition procedure overwrites any stored system information.
On the other hand, a UE verifies that stored system information remains valid by checking “SystemInfoValueTag” included in “SystemInformationBlockType1”. In a word, the UE considers previously stored system information to be invalid when “SystemInfoValueTag” in the “SystemInformationBlockType1” is different from the one of the stored system information, and thereby performs the system information acquisition procedure to reacquire system information. Additionally, the UE considers stored system information to be invalid after 3 hours from the moment that the system information was successfully confirmed as valid.
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-Advanced for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and/or transmitting.
Moreover, component carriers can be classified into a primary component carrier (PCC) and a secondary component carrier (SCC). The PCC is always activated, whereas the SCC is activated or deactivated according to specific conditions (e.g. an amount of data for transmission). The term “activation” means that transmission or reception of traffic data is performed or traffic data is ready for its transmission or reception. On the other hand, the term “deactivation” means that transmission or reception of traffic data is not permitted. In the deactivation, measurement is made or minimum information can be transmitted or received. In addition, a component carrier set to a secondary component carrier can be changed to a primary component carrier.
Note that, in the LTE system, the system information reception/acquisition is defined for the UE having only one connection to a single cell with a single component carrier. However, in the LTE-Advanced system, there is no system information reception mechanism defined for the UE having additional connections to additional cells with different component carriers. The applicant notices that an UE under carrier aggregation may encounter system information reception problems as below based on a direct image on a basis of a combination of the prior art LTE and LTE-Advanced system.
Consider a scenario that the network (e.g. an eNB) provides system information of a secondary component carrier to the UE with a dedicated signaling when the secondary component carrier is configured to the UE. Thus, the UE does not receive the system information of the secondary component carrier from a broadcast signaling on the secondary component carrier. The UE maintains the system information of the secondary component carrier valid for 3 hours when the system information of the secondary component carrier is received, and considers that the system information of the secondary component carrier is invalid after three hours. The UE has no valid system information of the secondary component carrier after three hours, and does not know how to obtain it for updating the system information of the secondary component carrier.
In another scenario, the UE updates system information of a secondary component carrier via a dedicated signaling from the network. However, when the secondary component carrier is configured to be the primary component carrier, the UE does not know how to obtain the system information of the primary component carrier (namely the original secondary component carrier) for system information update.